We investigated the response inhibition function of the prefrontal cortex associated with the go/no-go task using functional magnetic resonance imaging in five human subjects. The go/no-go task consisted of go and no-go trials given randomly with roughly equal probability. In go trials a green square was presented and the subjects had to respond by promptly pushing a button using their right or left thumbs, but in no-go trials a red square was presented and subjects were instructed not to respond. When brain activity in no-go trials is dominant over that in go trials in areas in the prefrontal cortex, this no-go dominant brain activity would reflect the neural processes for inhibiting inherent response tendency. We used a new strategy of image data analysis by which transient brain activity in go or no-go trials can be analysed separately, and looked for the prefrontal areas in which the brain activity in no-go trials is dominant over that in go trials. We found the no-go dominant foci in the posterior part of the right inferior frontal sulcus reproducibly among the subjects. This was true whether the right or left hand was used. These results suggest that this region in the prefrontal cortex is related to the neural mechanisms underlying the response inhibition function.